The present invention relates to powdered metal compacting presses and more particularly to a lower punch assembly or tooling for rotary table compacting presses.
A wide variety of small, metal parts are made employing powder metallurgy techniques. Powder metallurgy, basically, involves the production of metal powders which are consolidated to a desired density, shape and cohesion to form a part. The part is subsequently subjected to a heating process known as sintering. Sintering may involve the formation of liquid phase or may be carried out below the melting point of all the metal powder constitutents. Powder metallurgy permits the fabrication of refractory or reactive metals, provides for the homogeneous combination of dissimilar materials and permits the production of metal parts of controlled porosity or permeability. Powder metallurgy also permits the production of large numbers of small parts at significantly lower cost when compared to other conventional techniques, such as casting, forging or machining. Typically, the maximum weight of a part which may be made by powder metallurgy techniques is on the order of one pound. Parts may be fabricated employing such techniques from copper, iron, steel, bronze and aluminum powders.
Various forms of compacting presses have been developed for use in powder metallurgy processes. Examples of such presses may be found in U.S. Pat. No. 2,762,078, entitled MOLDING PRESS WITH ADJUSTABLE CORE ROD and issued on Sept. 11, 1956, to Haller; U.S. Pat. No. 3,172,156, entitled COMPPACTING PRESS and issued on Mar. 9, 1965, to Belden; and U.S. Pat. No. 3,868,201, entitled POWDERED METAL PRESS and issued on Mar. 25, 1975, to Jacobson et al. The presses disclosed in these patents, basically, include a platen supporting a die cavity, a core rod, a lower punch sleeve and an upper ram which also supports a punch sleeve.
The press disclosed in the Haller patent includes a core rod secured to a piston which is disposed within a cylinder. The piston cylinder assembly is a double-acting arrangement, and fluid under pressure enters ports at each end of the cylinder. An accumulator supplies fluid to the cylinder. The press is operable so that the core piece will move downwardly during the compaction stroke when the upper punch is moved relative to the lower punch. During ejection, the lower punch and core piece are advanced upwardly.
The above presses all employ relatively movable platens and/or rams and punches which shift only about a vertical axis. Other forms of compacting presses have been developed which are generally referred to as rotary table presses. These presses employ generally circular upper and lower tables or die head assemblies which are positioned in a superimposed relationship. The head assemblies support a plurality of circumferentially positioned dies, lower punch assemblies and upper punch assemblies. As the tables are rotated about a vertical, central axis, the upper and lower punches are progressively moved towards each other to compact powder metal disposed within the die cavities. The punches are subsequently moved apart, and the parts are ejected after compaction. The upper and lower punch assemblies each include a shank member which defines a heel or cam follower surface. The follower surface engages a generally circular cam track or ramp-like structure. As the tables rotate, the cam track reciprocates the punches to achieve compaction and ejection.
When producing certain powder metal parts, such as sleeves or bushings, excessive ejection loads may be encountered. The metal, when compacted within the die cavity, is pressed against the core rod. During ejection, excessive frictional forces are generated as the lower punch sleeve is moved upwardly on the core rod to force the compressed metal parts out of the die cavity. Significant loads are imparted to the tooling which can reduce reliability and result in tooling failure. Also, the shank members of the tooling which are shifted vertically and to which the punches are secured are fixed in the table structure for vertical movement only. The heels slide on the cam track surface. At operating speeds, significant heat is generated, and the cam tracks and/or shank members are subject to extremely high wear. Typically, the cam tracks are fabricated from a bronze material. Such wear has an adverse effect on reliability and limits the number of parts which may be formed before the cam track and/or shank must be replaced.
A need exists for tooling adapted to rotary table machines whereby the ejection forces may be significantly reduced and/or whereby the high wear between the heel of the shank and the cam surface may be eliminated.